Bone plate assembly with plates that ratchet together

ABSTRACT

A bone plate assembly is disclosed which includes at least one plate segment having at least one aperture extending therethrough for receiving a head portion of a bone screw, and a structure supported by the plate segment and intersecting the aperture for retaining the head portion of the bone screw with respect to the plate segment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/586,083, which is a continuation-in-part of U.S. patent applicationSer. No. 12/724,420, filed Mar. 15, 2010, now U.S. Pat. No. 8,262,711issued on Sep. 11, 2012, which claims the benefit of priority to U.S.Provisional Patent Application Ser. No. 61/160,154, filed Mar. 13, 2009,each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to implantable orthopedic appliances, andmore particularly, to a dynamic bone plate assembly and to structureassociated with the bone plate assembly for retaining bone screwsassociated therewith.

2. Description of the Related Art

A variety of implantable orthopedic devices are known in the art forassisting recovery following trauma or injury. Of such devices, many aredirected to relatively rigid devices that force substantial loadtransfer from the anatomical structure, for example, from the vertebralcolumn. Applicant recognizes that such load transfer inhibits desirableloading of the anatomical structure. In the case of bony tissue,insufficient loading will inhibit, reduce or prevent ossification of thestructure, the concept of which is described by and known as “Wolff'sLaw.”

Accordingly, Applicant recognizes that it is desirable to provideorthopedic appliances that provide for controlled load sharing, whileproviding support necessary to prevent damage to a bone graft and/orother anatomical structure, to allow for healing. Applicant alsorecognizes that it is desirable to provide orthopedic appliances thatare versatile and can provide adaptability to a variety of situations.Applicant further recognizes that it is desirable to provide at leastone locking feature to inhibit unintentional backing out of fasteners,such as bone screws. The present invention provides solutions for theforegoing.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, a vertebral columnconstruct for stabilizing a segment of a vertebral column is provided,having a first plate segment, a second plate segment connected to thefirst plate segment, and a spring connected between adjacent platesegments. An engagement member connected between the first and secondplate segments can also be provided. Alternatively, the separateengagement member can be omitted if sufficient stability is otherwiseprovided, such as by the spring or another element.

The spring can be adapted and configured to provide a predeterminedpreload between the first and second plate segments. Accordingly, thespring can be shaped, dimensioned and formed from a material appropriateto achieve the predetermined preload, in combination with othercomponents of the construct. Such a preload can advantageously enhancefusion across a bone graft

Alternatively, the spring can be adapted and configured to resist, by apredetermined degree, loading between the first and second platesegments.

A cam can be provided on one of the first and second plate segments, andbe moveable between engagement with cam surface in connection with theother of the first and second plate segments, and disengagementtherefrom, wherein engagement between the cam and the cam surfaceprevents dynamic loading of the spinal segment, between the first andsecond plates.

The cam can be configured such that the position of the cam determineswhether the preload exerted by the spring is transferred through theconstruct or transferred to the segment of the vertebral column to whichthe construct is attached. The cam can be adapted and configured toadjust preload applied between segments, by adjusting tension in thespring. The spring can be an arcuately bent rod or bar. The spring canbe made from a shape memory alloy. The spring can be engaged withgrooves in one of the plate segments, the grooves being configured suchthat outward application of force by the spring is resolved as a netaxial contractive force between the first and second plate segments.

A common upper plate can be provided, and connected to the first andsecond plate segments. The upper plate and at least one of the first andsecond plate segments can be adapted and configured for a substantiallylinearly translatable connection therebetween. The upper plate andslideably connected bottom plate segment can be connected by amechanical interlock. The mechanical interlock can include a dovetail ora pin and slot configuration.

A third plate segment can be provided and connected to at least one ofthe first and second plate segments by a spring, and optionally anengagement member. Fourth, fifth, sixth and subsequent plate segmentscan also be provided.

In accordance with the invention, at least two plate segments can beprovided, and the construct can be adapted and configured such that aconnection spanned between first and second plate segments is selectablebetween static and dynamic configurations. In accordance with theinvention, at least three plate segments can be provided, spanning twoconnections, respectively, and the construct can be adapted andconfigured such that each of the two connections spanned is selectablebetween static and dynamic configurations.

In accordance with another aspect of the invention, a vertebral columnplate system construct for stabilizing a segment of a vertebral columnis provided having a first plate segment, a second plate segmentconnected to the first plate segment, a spring element connected betweenadjacent plate segments, adapted and configured for providing apredetermined preload between adjacent plate segments, to enhance spinalfusion, an upper plate connected to the first and second plate segments,and a cam provided on one of the first and second plate segments,moveable between engagement with cam surface in connection with theother of the first and second plate segments, and disengagementtherefrom, wherein engagement between the cam and the cam surfaceprevents dynamic loading of the spinal segment, between the first andsecond plates. Further, an engagement member connected between adjacentplate segments can be provided.

In accordance with the invention, the cam surface can be provided on theother of the first and second plates. Alternatively, the cam surface canbe on the upper plate. In such an arrangement, the upper plate and theother of the first and second plates can be substantially rigidlyconnected to one another.

In accordance with a further aspect of the invention, a method ofimplanting a vertebral column construct on a spinal segment is provided,the method including, in any order, securing each of a plurality ofplates of the construct to respective vertebrae, determining whether toapply a preload between first and second levels of vertebrae, andapplying a first preload between said first and second levels ofvertebrae. The step of applying the first preload can include rotating afirst cam of the dynamic vertebral column construct in a firstdirection.

The method can further include the steps of evaluating efficacy of thefirst preload, and applying a second preload, in place of the firstpreload, between said first and second levels of vertebrae, the secondpreload being different from the first preload. The second preload beinggreater than the first preload. Alternatively, the second preload can beless than the first preload.

The step of applying a second preload can include rotating a first camin a second direction, different from the first direction. The methodcan further include the steps of determining whether to apply a preloadbetween first and second levels of vertebrae, and applying a thirdpreload between said second and third levels of vertebrae. The step ofapplying the third preload can include rotating a second cam of thedynamic vertebral column construct in a first direction.

The method can further comprises the steps of evaluating efficacy of thethird preload, and applying a fourth preload, in place of the thirdpreload, between said second and third levels of vertebrae, the fourthpreload being different from the third preload. The step of applying thefourth preload can include rotating a second cam in a second direction,different from the first direction.

Constructs in accordance with the invention, additionally oralternatively, can be configured to provide a predetermined amount ofresistance to contraction and/or to bending between adjacent platesegments thereby allowing for a predetermined amount of load sharingbetween the construct and the vertebral column segment.

In accordance with the invention, the engagement members, if provided,can be symmetrically arranged in the construct with respect to alongitudinal axis thereof. Moreover, two laterally opposed, springs canbe provided in the construct and can be arranged substantiallysymmetrically with respect to a longitudinal axis of the construct.

In accordance with the invention, a plurality of screws can be providedfor engaging the construct to the vertebral column segment. The screwscan include a slot or other feature for accepting an engagement elementfor inhibiting unintentional backout of the screws. In accordance withthe invention, one or more of the plate segments can be embodied so asto include respective upper and lower portions.

A plurality of spring elements can be provided for assembly with platesegments, the spring elements being provided in a range of stiffnesses,allowing for selectability of contractive force, or preload, of theconstruct and/or selectability of resistance to contraction, and/orbending stiffness of the construct, if so-embodied. The engaging elementcan be received in a corresponding recess provided in each plate segmentconnected by the engagement member.

In accordance with an embodiment of the subject invention, there isprovided a bone plate assembly that includes at least one plate segmenthaving at least one aperture extending therethrough for receiving a headportion of a bone screw, and means supported by the plate segment andextending into or otherwise intersecting the aperture for retaining thehead portion of the bone screw with respect to the plate segment.Preferably, the means for retaining the head portion of the bone screwis defined by a spring rod. The spring rod may be generally U-shaped orelongated. The elongated spring rod may include a central mountingportion flanked by at least one curved screw head retention portion.Preferably, the plate segment includes an upstanding yoke for supportinga central mounting portion of the spring rod.

It is envisioned that the aperture in the bone plate segment is definedat least in part by an upstanding peripheral wall, and a window isformed in the wall for accommodating passage of a retention portion ofthe spring rod. The assembly further includes a bone screw, and the headportion of the bone screw includes a reception groove for engagement bya retention portion of the spring rod. Alternatively, the head portionof the bone screw has an upper reception surface for engagement by aretention portion of the spring rod.

The subject invention is also directed to a dynamic bone plate assemblythat includes a plurality of interconnected plate segment each having apair of apertures extending therethrough for receiving a head portion ofa bone screw, and means supported by each plate segment and extendinginto or otherwise intersecting the apertures associated therewith forretaining the head portion of the bone screws with respect to the platesegment. Preferably, the dynamic bone plate assembly includes a pair ofouter plate segments and a central plate segment. In one version of thedynamic plate assembly, the means for retaining the head portion of thebone screws in each outer plate segment is a generally U-shaped springrod, and the means for retaining the head portion of the bone screws inthe central plate segment is an elongated spring rod.

In another version of the dynamic plate assembly, the means forretaining the head portion of the bone screws in the central platesegment is an elongated spring rod having a central mounting portionflanked by oppositely curved screw head retention portions. In yetanother version of the dynamic bone plate assembly, the means forretaining the head portion of the bone screws in each of the three platesegments is an elongated spring rod. In still another embodiment of thesubject invention, the means for retaining the head portion of the bonescrew is defined by a retention clip that extends into the aperturethrough a side wall of the plate segment. In either of theseembodiments, the retaining rods can have circular or squarecross-sections, and can be formed by any conventional metal formingprocess.

The subject invention is also directed to a dynamic bone plate assemblythat includes at least first and second plate segments adapted andconfigured for movement relative to one another from a spaced apartposition and an approximated position, and ratchet means for allowingthe first and second plate segments to move from the approximatedposition while preventing the first and second plate segments frommoving toward a spaced apart position. Preferably, the ratchet meansincludes a ratcheting pawl member operatively associated with the firstplate segment and a rack of ratchet teeth provided on the second platesegment for interacting with the pawl member.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and are intended toprovide further explanation of the invention claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute partof this specification, are included to illustrate and provide a furtherunderstanding of the systems, devices, kits and related methods of theinvention. Together with the description, the drawings serve to explainthe principles of the invention, wherein:

FIGS. 1A and 1B are, respectively, an isometric line drawing and anisometric rendering showing internal structure, of a representativeembodiment of a dynamic vertebral column plate system and accompanyingscrews, in accordance with the present invention, wherein the vertebralcolumn plate system is shown in an extended state;

FIGS. 1C and 1D are, respectively, an isometric rendering showinginternal structure and an isometric line drawing of a representativeembodiment of a dynamic vertebral column plate system and accompanyingscrews, in accordance with the present invention, wherein the vertebralcolumn plate system is shown in a collapsed state;

FIGS. 2A and 2B are, respectively, an isometric line drawing and anisometric rendering showing internal structure, of the dynamic vertebralcolumn plate system of FIGS. 1A and 1B, shown without accompanyingscrews, in accordance with the present invention;

FIGS. 3A and 3B are, respectively, a top line drawing and a toprendering showing internal structure, of the dynamic vertebral columnplate system of FIGS. 1A and 1B, shown with accompanying screws;

FIG. 3C is a top line drawing of the dynamic vertebral column platesystem of FIGS. 1A and 1B, shown without the accompanying screws;

FIGS. 4A and 4B are, respectively, an end line drawing and an endrendering showing internal structure of the dynamic vertebral columnplate system of FIGS. 1A and 1B, shown with accompanying screws;

FIGS. 5A and 5B are, respectively, a side line drawing and a siderendering showing internal structure, of the dynamic vertebral columnplate system of FIGS. 1A and 1B, shown with accompanying screws;

FIG. 6A is a bottom line drawing of the dynamic vertebral column platesystem of FIGS. 1A and 1B, shown with accompanying screws;

FIG. 6B is a bottom line drawing of the dynamic vertebral column platesystem of FIGS. 1A and 1B, shown without the accompanying screws;

FIGS. 7A and 7B are, respectively, a line drawing and a renderingillustrating a detail view of a portion of the dynamic vertebral columnplate system of FIGS. 1A and 1B, shown with an accompanying screw;

FIGS. 8A and 8B are, respectively, isometric line drawings of top andbottom surfaces of an upper plate segment of the dynamic vertebralcolumn plate system of FIGS. 1A and 1B;

FIG. 9 is an a isometric line drawing, showing the lower surface of theupper plate segments of the dynamic vertebral column plate system ofFIGS. 1A and 1B;

FIG. 10 is an a isometric line drawing, showing the upper surface of thelower plate segments of the dynamic vertebral column plate system ofFIGS. 1A and 1B;

FIGS. 11A and 11B are, respectively, a line drawing and a renderingillustrating a screw and a retaining clip in accordance with theinvention for use with the dynamic vertebral column plate system ofFIGS. 1A and 1B;

FIG. 11C is a line drawing of the screw of FIGS. 11A and 11B, shownwithout the retaining clip;

FIG. 12 is a top isometric view of the screw of FIGS. 11A, 11B and 11C,shown without the retaining clip, and illustrating a socket portionthereof;

FIG. 13 is an isometric line drawing showing an engagement member forjoining adjacent plate segments of the dynamic vertebral column platesystem of FIGS. 1A and 1B;

FIG. 14 is an isometric line drawing showing spring members for joiningadjacent plate segments of the dynamic vertebral column plate system ofFIGS. 1A and 1B;

FIG. 15A is a top view of a spring member of FIG. 14;

FIG. 15B is a bottom view of the spring member of FIG. 15A;

FIG. 15C is a front isometric view of the spring member of FIG. 15A;

FIG. 15D is a an enlarged partial view of the spring member of FIG. 15A,illustrating a central bend thereof;

FIG. 15E is a left side view of the spring member of FIG. 15A;

FIG. 15F is a right side view of the spring member of FIG. 15A;

FIG. 16-29 illustrate various views of another exemplary embodiment of adynamic vertebral column plate system in accordance with the invention,having arcuately bent rod or bar-shaped springs and an integral camelement;

FIG. 16 is an isometric view of the plate construct in accordance withthis embodiment, shown in an expanded condition;

FIG. 17 is a side view of the plate construct, shown in an expandedcondition;

FIG. 18 is an isometric view of the plate construct, shown in acontracted condition;

FIG. 19 is a side view of the plate construct, shown in a contractedcondition;

FIG. 20 is a bottom isometric view of the plate construct, shown in anexpanded condition;

FIG. 21 is a bottom isometric view of the plate construct, shown in acontracted condition;

FIGS. 22A-C are end views of the plate construct, illustrating engagingsteps between an upper plate and a lower end plate segment;

FIG. 23 is a partly exploded isometric view of the plate construct,illustrating internal components thereof and a tool for operating a camthereof;

FIG. 24 is a bottom isometric of the upper plate of plate construct;

FIG. 25 is an exploded view of the internal components of the plateconstruct;

FIG. 26 is an isometric view of the plate construct, shown in anexpanded condition with both cams rotated out of engagement withopposing recesses therefor, shown with the upper plate removed forvisibility;

FIG. 27 is top view of an end portion of the plate construct with theillustrated cam held in an opposing recess, maintaining the expandedcondition of the plate, shown with the upper plate removed forvisibility;

FIG. 28 is an isometric view of the plate construct with both camsrotated out of engagement with the opposing recesses therefor, shown ina contracted condition, with the upper plate removed for visibility;

FIG. 29 is top view of an end portion of the plate construct with theillustrated cam rotated out of engagement with the opposing recessestherefor, maintaining the expanded condition of the plate, shown in acontracted condition, with the upper plate removed for visibility;

FIGS. 30A-C illustrate implantation steps of the dynamic vertebralcolumn plate system construct of FIGS. 16-29, but which steps applygenerally to other embodiments of the invention;

FIG. 30A illustrates the construct during insertion of a final screw forengaging the attached vertebral segment;

FIG. 30B illustrates the construct during rotation of a cam thereof,with a tool therefor;

FIG. 30C illustrates the construct following attachment to the vertebralsegment and rotation of both cams from the opposing recesses therefor,shown with the upper plate removed for visibility;

FIGS. 31A-H are side and cross-sectional views of various screwconfigurations for use with the dynamic vertebral column plate systemsof the invention;

FIG. 32A is an isometric view of a dynamic vertebral column plate systemconstruct in accordance with the invention, having two levels of platesegments;

FIG. 32B is an isometric view of a dynamic vertebral column plate systemconstruct in accordance with the invention, having four levels of platesegments;

FIGS. 33-39 various views of further exemplary embodiment of a dynamicvertebral column plate system construct in accordance with theinvention, having band-shaped springs and an integral cam elementconfigured to permit a plurality of selectable preloads;

FIG. 33 is an isometric view of the construct of this embodiment, shownin an expanded condition;

FIG. 34 is an isometric view of the construct of this embodiment, shownin a contracted condition;

FIG. 35 is an isometric view of the construct of this embodiment, shownin an expanded condition, with the upper plate removed for visibility;

FIG. 36 is a bottom isometric view of the upper plate of this embodimentof the construct;

FIG. 37 is a top view of the construct of this embodiment shown in anexpanded condition, with the upper plate removed for visibility;

FIG. 38 is a top view of the construct of this embodiment shown in acontracted condition, with the cams in one position for applying acorresponding preload to a spinal segment, and with the upper plateremoved for visibility;

FIG. 39 is a top view of the construct of this embodiment shown in acontracted condition with the cams in another position (as compared withFIG. 38), for applying a different corresponding preload to a spinalsegment, also shown with the upper plate removed for visibility;

FIG. 40 is a perspective view of another dynamic spinal plate assemblyconstructed in accordance with a preferred embodiment of the subjectinvention, which includes structure for retaining bone screws;

FIG. 41 is a top plan view of the spinal plate assembly shown in FIG.40, with the upper plate portion removed to show the screw retentionfeatures of the plate assembly;

FIG. 42 is a localized view of the spinal plate assembly shown in FIG.41, illustrating the screw retention feature, wherein the end portion ofthe generally U-shaped spring rod is engaged in a channel formed in thehead of a bone screw to prevent the bone screw from backing out;

FIG. 43 is a localized view of the spinal plate assembly shown in FIG.41, illustrating the screw retention feature, wherein the end portion ofa central spring rod is engaged with an upper surface of the head of abone screw to prevent the bone screw from backing out;

FIG. 44 is a plan view of another spinal plate assembly constructed inaccordance with a preferred embodiment of the subject invention, whichincludes central screw retention structure in the form of a shapedspring rod;

FIG. 45 is a localized perspective view of the central portion of thespinal plate assembly shown in FIG. 44, illustrating a shaped spring rodhaving a central mounting portion flanked on each side by a curved screwhead retention portion;

FIG. 46 illustrates the degree of flexure of the curved screw headretention portion of the shaped spring rod shown in FIG. 45;

FIG. 47 illustrates the engagement of the curved screw head retentionportion of the spring rod with a retention channel formed in the head ofa bone screw;

FIG. 48 is a plan view of a section of the spinal plate assembly of thesubject invention, illustrating a ratchet mechanism that allows twoplate segments to move toward one another to shorten the length of theplate assembly, while preventing the two segments from moving apart fromone another;

FIG. 49 is an enlarged localized view of the ratchet mechanism shown inFIG. 48 when the plate segments are spaced apart from one another; and

FIG. 50 is a localized view of the ratchet mechanism showing the platesegments in an approximated position, in which the ratchet arm preventsthe plate segments from moving apart from one another;

FIG. 51 is a plan view of yet another embodiment of a dynamic spinalplate assembly constructed in accordance with a preferred embodiment ofthe subject invention, which includes screw retention structure in theform of three transverse spring rods for retaining bone screwsassociated with each segment of the plate assembly by engaging uppersurfaces of the heads of the bone screws;

FIG. 52 is a cross-sectional view taken along line 52-52 of FIG. 51;

FIG. 53 is a plan view of yet another embodiment of a dynamic spinalplate assembly constructed in accordance with a preferred embodiment ofthe subject invention, which includes screw retention structure in theform of three transverse spring rods for retaining bone screwsassociated with each segment of the plate assembly by engaging retentionchannels formed in the heads of the bone screws;

FIG. 54 is a localized view of section of the spinal plate assemblyshown in FIG. 53 illustrating the position of the spring rod in theabsence of a bone screw;

FIG. 55 is a cross-sectional view taken along line 55-55 of FIG. 53illustrating the engagement of a spring rod in the retention channel ofthe head of a bone screw;

FIG. 56 is a perspective view of a section of a bone plate with anassociated bone screw, together with a retention clip configured toengage the head of the bone screw through the side wall of the plate;and

FIG. 57 is a perspective view showing the retention clip engaging thehead of the bone screw through the side wall of the plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to preferred embodiments of theinvention, an example of which is illustrated in the accompanyingdrawings.

The devices and methods presented herein may be used for stabilizationof a segment of the vertebral column during spinal fusion followingsurgery.

With reference to the figures and as seen, for example, in FIGS. 1A and1B, a dynamic vertebral column plate system for stabilizing a segment ofa vertebral column is able to be assembled into a plate construct 100for attachment to a vertebral column segment. Such constructs can beprovided to a user (such as a surgeon) already assembled, or can beassembled by the user, for example. The plate system includes a firstend plate segment, having upper and lower portions 110 a and 120 a, asecond end plate segment having upper and lower portions 110 c and 120 cconnected to and arranged opposite the first plate segment. Asillustrated, an intermediate plate segment having upper and lowerportions 110 b and 120 b can be provided. In accordance with furtheraspects of the invention, additional intermediate plate segments canadditionally be provided, yielding a total of 3, 4, 5, 6, 7, 8 or moreplate segments in the construct 100 formed from the components of thesubject system.

In the illustrated embodiment, an engagement member 140 and springelements 130 are provided between and connect adjacent plate segments,forming the plate construct 100. Although one engagement member 140 andtwo springs 130 are illustrated between each adjacent pair of platesegments, it is to be understood that any suitable number of suchelements can be provided. It is particularly conceived that twolaterally opposed engagement members 140 can be additionally oralternatively provided laterally distal to the springs 130. In such anembodiment, it is conceived that it may prove necessary to provideadditional material along the lateral edges of the plate segments 110,120 to provide structural support and/or simply to provide space forholding the additional engagement members.

The springs 130 are adapted and configured to provide a predeterminedamount of contractive force, or preload, of the construct 100. Inaccordance with alternate embodiments the springs 130 can be adapted andconfigured to provide a predetermined amount of bending stiffnessbetween adjacent plate segments, thereby allowing for a predeterminedamount of load sharing between the construct 100 and the vertebralcolumn segment to which it is attached.

As can be seen in FIGS. 1A and 1B, a plurality of screws 150 areprovided for anchoring the construct 100 into the bone. Apertures 113 aare provided in upper plate portion 110 a, 110 b, 110 c, in which thehead of the screws 150 rest. A groove 155 is provided in the head of thescrew 150 for receiving a locking element, such as the retaining clip159, which is best seen in FIGS. 11A and 11B. The locking element can beany suitable element, including but not limited to a resilient o-ring,cir-clip, or another suitable element, such as a latching toroidal coilavailable from Bal Seal Engineering, Inc. of Foothill Ranch, Calif.,USA. The locking element can be formed of any suitable material, such asa metal, metal alloys, an elastomeric material, silicone,polychloroprene (e.g. Neoprene), or a plastic material such aspolyetheretherketone (PEEK), for example. The locking element, carriedby the screw can seat in a groove provided in the construct being used.

As seen in FIG. 1B, as well as in FIGS. 1C, 8B, 9 and 10, springengagement members or bosses 115, 125 can be provided in connection withor integrally with the plate segments, such as with upper plate portion110 a or lower plate portion 120 a, respectively, for engaging thesprings 130. Similarly, the engagement members 140 are secured toadjacent plates by a recess 117, 127 provided in each respective upperplate portion 110 a-c and lower plate portion 120 a-c. The recesses 117,127 are shaped with a corresponding partial “I” shape to capture theengagement members 140, and to allow for axial motion between the plateportions 110, 120 and the engagement members 140. Accordingly, thetransverse section of the recess 117, 127 can be deeper than that of theengagement member 140 to allow for axial motion. Moreover, it is to beunderstood that various shapes of engagement members 140 can be used,and are not be limited solely to the shape illustrated.

Although illustrated as independent components, it is to be understoodthat in alternative embodiments, engagement members 140 can beintegrally formed with one plate, fitting into a corresponding recess117, 127 in an adjacent plate. Accordingly, relative motion betweenplate segments is allowed, without necessitating manufacture andassembly of separate components. In line with such embodiments, it isparticularly conceived that any permutation of arrangements of separateor integral engagement members 140 is possible, with any suitable numberof engagement members 140 being provided between adjacent plates.

The round spring engagement members or bosses 115, 125 allow forrelative movement of the springs when the construct 100 is subjected todifferent loading conditions, such as axial tensile or compressiveforces or lateral bending (in a plane that is substantially parallel tothe plate surface and parallel to the longitudinal axis of theconstruct, for example). Alternatively, the bosses 115, 125 can be anysuitable shape, including but not limited to elliptical, oblong,polygonal (e.g., square, hexagonal). Shapes of bosses 115, 125 thatinhibit rotation thereabout can enhance lateral stability of theconstruct 100. A relatively shallow recess 119 is provided in one ormore of the upper plate portions 110 a-c and lower plate portions 120a-c, as best seen in FIG. 8B. The recesses 119 are configured to provideroom for elastic deformation of the springs 130 under the aforementionedaxial compression and/or bending conditions.

Upper and lower portions of the plate segments, such as upper plateportion 110 a and lower plate portion 120 a, can be mutually secured inany suitable manner, including but not limited to welding, mechanicalfasteners, solders, adhesives, epoxy materials, mechanical interlockfeatures or the like.

As mentioned above, FIGS. 2A and 2B are, respectively, an isometric linedrawing and an isometric rendering showing internal structure of thedynamic vertebral column plate system of FIGS. 1A and 1B, shown withoutaccompanying screws, in accordance with the present invention. FIGS. 3Aand 3B are, respectively, a top line drawing and a top rendering showinginternal structure of the dynamic vertebral column plate system of FIGS.1A and 1B, shown with accompanying screws. FIG. 3C is a top line drawingof the dynamic vertebral column plate system of FIGS. 1A and 1B, shownwithout the accompanying screws. FIGS. 4A and 4B are, respectively, anend line drawing and an end rendering showing internal structure of thedynamic vertebral column plate system of FIGS. 1A and 1B, shown withaccompanying screws. FIGS. 5A and 5B are, respectively, a side linedrawing and a side rendering showing internal structure, of the dynamicvertebral column plate system of FIGS. 1A and 1B, shown withaccompanying screws.

FIG. 6A is a bottom line drawing of the dynamic vertebral column platesystem of FIGS. 1A and 1B, shown with accompanying screws. FIG. 6B is abottom line drawing of the dynamic vertebral column plate system ofFIGS. 1A and 1B, shown without the accompanying screws. FIGS. 7A and 7Bare, respectively, a line drawing and a rendering illustrating a detailview of a portion of the dynamic vertebral column plate system of FIGS.1A and 1B, shown with an accompanying screw. FIGS. 8A and 8B are,respectively, isometric line drawings of top and bottom surfaces of anupper plate segment of the dynamic vertebral column plate system ofFIGS. 1A and 1B. FIG. 9 is an a isometric line drawing showing the lowersurface of the upper plate segments of the dynamic vertebral columnplate system of FIGS. 1A and 1B, and FIG. 10 is an a isometric linedrawing, showing the upper surface of the lower plate segments of thedynamic vertebral column plate system of FIGS. 1A and 1B.

As best seen in FIG. 3C, for example, the lower plate portions 120 a-cof each plate segment include smaller apertures 123 a, b or c,respectively for the screws 150 than the apertures 113 a-c provided,respectively in the upper plate portions 110 a-c. This allows firmengagement of the construct 100 to the vertebral column, with the largerapertures 113 a-c allowing space for inserting the retaining clip 159.

As seen best in FIGS. 11A-11D, the screws 150 illustrated can includeexternal threads 151 thereon for securely engaging bone. A proximalgroove 155 accepts a retaining clip 159 for facilitating engagement withthe construct 100. As seen in FIG. 12, the screw 150 can include asocket portion 153 and internal threads 157 provided therein tofacilitate removal of the screw 150 from the bone, if necessary ordesired. Such threads 157 are preferably opposite in directionality tothe threads 151 of the screw 150, so that as the screw is being removed,the extraction tool does not disconnect itself from the screw 150.

As best seen in FIG. 13, the engagement member 140 is shaped in thisembodiment substantially as a solid “I-beam.” Any of a variety ofmaterials can be used, including but not limited to stainless steel,titanium alloys, nickel alloys such as Nitinol, polymeric materials,ceramic materials or composite materials, for example. The shape of theengagement member 140, and particularly the web portion 143 thereof,provides resistance to, but can allow, if so-embodied, a predeterminedamount of bending of a construct created therewith.

In accordance with a preferred embodiment, the plate segments move in anaxial direction (parallel to the longitudinal axis of the construct100), guided by the engagement members 140. The springs 130 exert acompressive force between segments of the construct 100, while theengagement members 140 help stabilize the construct 100. In suchembodiments, the engagement members 140 are preferably relativelystrong, and stiff (i.e. resistant to bending forces).

Alternatively, if embodied to allow bending of the construct 100, due tothe placement of the springs 130 with respect to the engagement member140, lateral bending (roughly in the plane of the plate segments 110,120, but parallel to the longitudinal axis thereof) would generally beless than in the direction perpendicular thereto (out of the plane ofthe plate segments 110, 120 (but still in a plane parallel to thelongitudinal axis of the construct). The stiffness of the engagementmember 140 in such embodiments can be selected by varying the materialproperties thereof, by changing the composition of the material,treating the material, or by altering the shape thereof—particularly thecross-sectional shape to alter the area moment of inertia thereof.

As seen in FIGS. 14 and 15A-15F, the spring elements 130 includeengagement apertures 135 for mating with the spring engagement members115 formed on the upper plate portions 110 a-c and spring engagementmembers 125 formed on the lower plate portions 120 a-c. The springelements 130 can be formed of any suitable material, including but notlimited to stainless steel, titanium alloys, nickel alloys such asNitinol, polymeric materials, ceramic materials or composite materials,for example. The stiffness of the spring elements 130 can be selected byvarying the material properties thereof, by changing the composition ofthe material, treating the material, or by altering the shape thereof.With respect to the springs 130, the nature of the integral bend and thecross-section of the component in that area can be altered to increaseor decrease the stiffness thereof.

As illustrated, the spring 130 narrows to a relatively smallcross-sectional area. When axial compression is the main modality ofloading, the springs 130 can be provided pre-stressed, wherein therelaxed state of the spring results in a shorter length of the construct100 than the pre-stressed state. In such embodiments, the construct 100can be provided with removable spacers 160 (FIG. 1C) between platesegments that are removed following attachment to the vertebral columnsegment. Thereafter, the springs 130 exert a constant axial compressiveforce on the vertebral column segment.

In accordance with the invention, the stiffness of the engagementmembers 140, springs 130, in conjunction with the materials of the platesegments 110, 120 are selected to provide a desired amount of flexion inthe construct when joined with a vertebral column segment. In accordancewith one aspect, devices in accordance with the invention allow forbetween about 0 and 5.0 mm, and preferably between about 1.0 mm to 3.0mm of axial contraction at each level, across each inter-vertebralspace. In accordance with another preferred aspect, the subject devicesallow for about 2.0 mm of axial contraction at each level. If desired,the characteristics of the construct can be varied at different levels,providing greater preload force, or alternatively resistance to axialcontraction and/or bending at one level than at another level, ifdesired.

The shape of the plate segments 110, 120, engagement members 140 andsprings 130 preferably result, when combined with the respectivevertebral column segment, in a curvature very close to the naturalcurvature of that vertebral segment. Other than providing a bias tomaintain pressure across the inter-vertebral spaces to promote fusion ofbone grafts, the curvature is preferably very close to that of thevertebral column segment to which it is to be attached.

Further, the spacing between adjacent plate segments can be selected asdesired, and can vary between adjacent levels, across consecutiveinter-vertebral spaces, for example. Such flexibility allows for moreversatility when used with a patient's individual anatomy.

Moreover, devices in accordance with the invention can be configured soas to provide preloading across an inter-vertebral space to facilitatespinal fusion. This is accomplished, for example, by providing a bias inthe curvature of the assembled construct 100. This can be achieved byproviding the engagement members 140 and/or springs 130 with a preformedbend. Such bend need only be slight to result in an effective bias.

Screws, such as screws 150, for use in conjunction with devices inaccordance with the invention can include any desired features known inthe art. Such screws can be adapted for fixed angle insertion orvariable angle insertion having an arcuate lower surface at the junctionof the plate segments 110, 120. Such screws can be self-tapping orself-drilling. Features of example screws for use with devices inaccordance with the invention are described below in connection withFIGS. 31A-H.

FIGS. 16-29 illustrate various views of another exemplary embodiment ofa dynamic vertebral column plate system construct in accordance with theinvention, designated generally by reference number 200. The construct200 has, among other features, arcuately bent rod or bar-shaped springs230 and an integral cam element 261 that permits use of the construct200 as either a static plate or dynamic plate, providing preload at oneor more levels of a spinal segment. Simply put, if the cam 261 is leftin a locked position (e.g., as shown in FIG. 23) following implantationor alternatively, unlocked prior to implantation, then no preload willbe applied to that respective level. If, however, the cam 261 is lockedduring implantation and unlocked following attachment to a spinalsegment, a preload, provided by a respective spring 230, will be appliedat that level.

The construct 200 includes a number of features analogous to theconstruct 100 discussed in connection with FIGS. 1-15F. For example, theconstruct 200 includes a plurality of apertures 223 a-c for acceptingscrews for connection with respective vertebrae, a plurality of lowerplate portions 220 a-c, engagement members or guides 240, and springs230 for applying preload at respective levels, although theconfiguration of these features may vary somewhat substantially fromthose of the construct 100, as will be described in more detail below.

Notable differences between the construct 100 discussed in connectionwith FIGS. 1-15F, and the construct 200 of FIGS. 16-29 include a unitaryupper plate 210, an integral cam 261 and associated features, adifferent arrangement of the springs 230 that apply a preload, ifdesired.

The unitary upper plate 210 of the construct 200, is distinct inconfiguration from the individual upper plate portions 110 a-c of theconstruct 100 of FIGS. 1-15F. The unitary upper plate advantageouslyenhances stability of the construct 200, and thus also any attachedspinal segment, while permitting linear translation of adjacent lowerplate segments 220 a, 220 b, 220 c, and therefore also permitting anaxial application of load across the attached spinal segment to promotefusion.

As can be seen particularly in FIGS. 22A, 22B and 22C, the end platesegments 220 a, 220 c are engaged with the upper plate 210 by way of afemale dovetail 228 formed in the lower plate segments 220 a, 220 c, anda male dovetail 218 formed on the upper plate 210. The dovetails 218,228 restrain the relative movement between the end plate segments 220 a,220 c and the top plate 210 along each axis except for along alongitudinal axis, which movement is restrained in expansion byengagement members 240 and springs 230, and restrained in contraction byinterference with adjacent plates, such as the intermediate plate 220 b.Engagement of the dovetail 218 of the upper plate 210 is permitted withthe provision a cutout 212, which allows for deflection of resultingforks 214 of the upper plate 210, surrounding the cutout 212, on whichthe dovetail 218 is formed.

As with the construct 100, engagement members 240 are provided, whichserve to promote stability of the construct 200 and to limit expansionof the construct 200 beyond a predetermined amount. The lower platesegments 220 a-c include slots 227 to accommodate the engagement members240, while the upper plate 210 includes corresponding slots 217 for thatpurpose. The upper plate 210 includes tail portions 216 that partiallydefine slots 217 therein for the engagement member 240, and permit closeengagement at lateral edges of the construct 200 between the upper plate210 and lower plate segments 220 a, 220 b, 220 c.

Various apertures 211 a, 211 b, 211 c are provided in the upper plate210 for respective purposes. A central aperture 211 c is provided topermit pinning of the lower intermediate plate segment 220 b to theupper plate 210 during assembly. Such a pin can be peened, welded orconnected to the upper and lower plates in another suitable manner. Sucha pin can be integrally formed, such as by casting and/or machining,with one of the lower intermediate plate segment 220 b and the upperplate 210, for example. Alternatively, any intermediate plate such asplate 220 b can be connected to the upper plate 210 in another manner,such as by a dovetail feature discussed in connection with the end platesegments 220 a, 220 c, for example.

Respective apertures 211 a, 211 b are provided to enable access to eachcam 261, to rotate the cam 261 between locked and unlocked positions, asillustrated in FIG. 30B, for example. Apertures 211 b are also providedin line with the spaces 291 a, 291 b between lower plate segments 220 a,220 b, 220 c, which apertures 211 b provide a viewing window of theinter-vertebral space, through the construct 200, so that a surgeon canview the relative spacing between lower plate segments 220 a, 220 b, 220c, and also the condition of a bone graft (of the vertebrae and anyfusion devices or materials), during and after attachment of theconstruct 200 to a spinal segment. A surgeon can therefore determine,based on his or her experience, whether or not that level of theconstruct should remain static or if the cam 261 should be unlocked toprovide a dynamic load application at that level. The surgeon may takevarious factors into account, including any gaps that he or she may seein the inter-vertebral space, between vertebrae and any fusionmaterials, for example.

Following implantation, a surgeon can elect to leave one or more of thecams 261 in the locked position, or alternatively can unlock one or morecams prior to implantation, causing the corresponding gap (e.g. 291 a,291 b) to close. In either case, that level of the construct 200 wouldbehave essentially as a static plate. More typically, however, followingimplantation, each of the cams 261 will be unlocked by turning the cam261 from its seat in recess 265, as shown in FIG. 26, for example. Atthat time, even if no visible contraction occurs, the spring 230 at thatlevel begins to exert force across the corresponding gap (e.g. 291 a),and therefore to the spinal segment, which will typically be a fusionbetween vertebrae.

In accordance with an alternative embodiment, the cam 261 can beprovided that is similar to the cam 561 discussed below in connectionwith the embodiment of FIGS. 33-39. Alternatively still, the cam 261 canbe configured and adapted to engage a pin at one position to stretch therespective spring 230, to thus effect an increased preload followingimplantation.

The springs 230 are configured as an arcuate rod or bar. As illustrated,the ends of the springs 230 are held in pins 231 that are translatablewith respect to slots 215 and 225, formed respectively in the upperplate 210 and lower plates 220 a, 220 c (See FIGS. 23 and 24).

At the maximum extent of expansion of the construct 200, illustrated forexample in FIGS. 16, 17, 20, and 23, gaps 291 a, 291 b between adjacentlower plate segments 220 a, 220 b and 220 c are also at their maximum,which is limited by the central spring 230 and the laterally placedU-shaped engagement members 240, which are engaged in recesses 117, 127formed in the top plate 210 and each of the bottom plate segments 220a-c, respectively. The cams 261, rotate on respective bosses 267 and intheir locked position, engage recesses 265 formed on a facing surface ofthe adjacent plate, maintaining a predetermined spacing. In addition toan aperture in the cam 261 for accommodating the boss 267, an aperture269 can be provided in the cam for engagement with a tool for rotatingthe cam 261.

The dimensions of the components can be selected to vary the amount ofspacing between adjacent plates, however, in accordance with onepreferred embodiment, the maximum spacing of the gaps 291 a, 291 b isabout 2.0 mm, for example, for use in a cervical spinal segment. Thisspacing can be selected to be smaller or larger, such as between 1.0 mmand 3.0 mm of translation, depending on the placement of the construct200 (or any other construct in accordance with the invention). That is,if used on a lumbar spinal segment, the construct can be configured soas to provide a larger maximum spacing between plate segments, forexample 3.0 mm or perhaps larger if indicated for a particularapplication. The maximum spacing 291 a, 291 b between plate segments 220a-c determines the maximum range of travel along which the spring 230can apply a preload to a level of the spine, such as across a fusion.

A block of bone, a fusion cage or other fusion material is typicallyinserted in place of a disc, between vertebrae that are to be fusedtogether and carries the bulk of load carried by the spine. Theconstruct 200, then provides stabilization to the spinal segment towhich it is attached while minimizing load transfer to the construct,which promotes proper fusion. The springs 230 also maintain a load onthe segment even in the absence of external load. In this manner, theconstruct 200 (and other constructs in accordance with the invention)advantageously permit settling of fusion materials, while minimizing anyspacing between adjacent vertebrae and the fusion materials, furtherenhancing fusion.

In the embodiment of the construct 200 of FIGS. 16-29, implantation ofwhich is illustrated in FIGS. 30A, 30B and 30C, the springs 230 arearcuately-shaped rod or bar elements, formed from a resilient material.In accordance with a preferred aspect, the springs 230 are formed of ashape memory alloy, such as Nitinol. In accordance with one aspect, thesprings 230 are linear in their natural state and are bent into theillustrated arcuate configuration upon assembly of the construct 200.The diameter of the springs 230 is selected based on the desired amountof force to be applied. Accordingly, the springs 230, in attempting torevert to their natural configuration, rotate in an outward arc,exerting initially a substantially laterally outward force through thepins 231 at the ends thereof to the outer plate segments 220 a, 220 c byway of the slots 225 formed therein.

The slots 215 formed in the underside of the top plate follow the arc ofthe pins 231 caused by the spring 230. The slots 225 in the lower endplate segments 220 a, 220 c are linear in configuration, with thelongitudinal component of the arc of travel of the pins 231 beingprovided in the translation of the plate segments 220 a, 220 cthemselves, in closing the gaps 291 a, 291 b. The linear configurationof the slots 225 of the lower end plate segments 220 a, 220 c in whichthe pins 231 ride, promote resolution of the generally arcuateapplication of spring force into an axial force, parallel to thetranslation of the end plate segments 220 a, 220 c. As can beappreciated, any transverse component of force applied by the springwill be applied symmetrically by each of the pins 231, which forces willtherefore cancel one another within the outer plate segments 220 a, 220c, and not result in any net external forces.

As configured, the slots 225 are not perfectly parallel to the edge ofthe plates 220 a, 220 c. The degree of angle of the slots 225 isprovided to increase the distance of translation of the outer platesegments 220 a, 220 c across which sufficient force application isapplied.

In accordance with the invention, a target force application can bebetween about 0 N and 90 N (between about 0-20 pounds-force). Inaccordance with one embodiment of the invention, a target forceapplication is between about 13 N and 44 N (between about 3-10pounds-force) for applications on a cervical vertebral segment.Alternatively, depending on the spinal segment, the target forceapplication can be greater or smaller. In accordance with anotherembodiment of the invention, a target force for application is betweenabout 44 and 89 N (between about 10-20 pounds-force) for thoracic orlumbar vertebral segments. As discussed herein, if resistance tocompressive forces are desired and application of a preload by any ofthe constructs described herein is not desired, then such target forceis 0N. Any application of force sufficient to safely achieve the desiredeffect is possible in accordance with the invention.

FIG. 26 illustrates the construct 200 in an expanded condition, justafter disengagement of the cams 261 from the opposing recesses 265. Asillustrated in FIGS. 28 and 29, in the absence of an attached spinalsegment, upon disengagement of the cam 261 from the opposing recess 265,the outer plate segments 220 a, 220 c are pulled inward by the action ofthe springs 230.

FIGS. 30A-C illustrate implantation of the dynamic vertebral columnplate system construct 200 of FIGS. 16-29 in various stages ofattachment to a spinal segment 90. FIG. 30A illustrates the construct200, in an expanded condition, attached to three vertebral bodies 91, 93and 95, and spanning two inter-vertebral spaces 92 and 94 of a spinalsegment 90, and insertion of a screw 150 with an insertion tool 81therefor. FIG. 30B illustrates the construct 200 during disengagement ofthe lower cam 261 with a tool 83 therefor. FIG. 30C is a plan view ofthe construct 200, with the upper plate 210 removed for visibility,following disengagement of each cams 261 from its respective opposingrecess 265. Force applied by the springs 230 is indicated by arrows,with resultant force applied to the spinal segment illustrated by arrowsparallel to the longitudinal axis thereof. As illustrated, the cams 261can't rotate fully away from the adjacent plate due to the position ofpins 231 following disengagement. However, as settling occurs and thepins 231 move laterally outward, the cam 261 can continue to rotate awayfrom the adjacent plate.

FIGS. 31A-H are side and cross-sectional views of various screwconfigurations for use with the dynamic vertebral column plate systemsof the invention. FIGS. 31A and 31B illustrate a screw 250 having aself-tapping end 254 and a head 258 permitting variable angle engagementwith an attached plate. A groove 255 is provided in the head 258 of thescrew 250 for receiving a locking element, which can be any suitableelement, including but not limited to a resilient o-ring, cir-clip, oranother suitable element, such as a latching toroidal coil availablefrom Bal Seal Engineering, Inc. of Foothill Ranch, Calif., USA. Thelocking element can be formed of any suitable material, such as a metal,metal alloys, an elastomeric material, silicone, polychloroprene (e.g.Neoprene), or a plastic material such as polyetheretherketone (PEEK),for example. The locking element, carried by the screw can seat in agroove provided in the construct being used.

As with the screw 150 discussed in connection with the embodiment ofFIGS. 1-15F, the screw 250 includes a socket 153 for engaging aninsertion tool for implantation, and internal threads 157 are preferablyprovided to facilitate removal of the screw 250, if necessary. FIGS. 31Cand 31D are side and cross-sectional views of a screw 350, having a head258 permitting variable angle engagement, and a self-drilling end 356.FIGS. 31E and 31F are side and cross-sectional views of a screw 450having a head 459 permitting only fixed-angle engagement with anattached plate, due to the trapezoidal cross-section thereof, ascompared with the more rounded cross-section of the head 258 of screws250 and 350. The screw 450 also includes a self-drilling end 356. FIGS.31G and 31H illustrate a screw 550 with a head 459 for fixed-angleengagement, and a self-tapping end 254.

FIG. 32A is an isometric view of a dynamic vertebral column plate systemconstruct 300 in accordance with the invention having two levels ofplate segments, 320 a, 320 b and a unitary upper plate 310. The internalcomponents can be any of those illustrated herein, but as illustrated,the construct 300 is provided with a spring arrangement similar to thatof the construct 200 described in connection with FIGS. 16-29.

FIG. 32B is an isometric view of a dynamic vertebral column plate systemconstruct 400 in accordance with the invention having four levels ofplate segments, 420 a, 420 b, 420 c and 420 d, and a unitary upper plate410. The internal components can be any of those illustrated herein, butas illustrated, the construct 400 is provided with a spring arrangementsimilar to that of the construct 200 described in connection with FIGS.16-29. As discussed above, the intermediate plates 420 a, 420 b can beconnected by way of a pin, or in an alternative manner.

In any case, it is generally preferred, but not required, that no morethan one lower plate segment (e.g. 420 a-d) be non-translatably securedto the upper plate 410. In the case of a two-level construct, one levelcan be pinned to the upper plate, or alternatively, both can beslideable with respect thereto. In the case of a three-level construct,as illustrated in FIGS. 16-29, the intermediate plate can benon-translatably secured by a pin or other feature. Although a dovetailfeature can be applied to intermediate plates, connection with one ormore pins may provide for easier assembly of the construct 400.Accordingly, in a four-level construct, as with construct 400, one ofthe intermediate plates, e.g., 420 b can be non-translatably pinned,while the other of the intermediate plates e.g., 420 c can be pinned byway of a slot 411 in the upper plate 410. Such a pin and slot 411configuration can additionally be applied to, or alternatively in placeof, any dovetail configuration described herein, if desired.

In accordance with the invention, the number of lower plates can beselected as desired. In practice, the number of lower plate levels thatwould typically be used would range from between two and six.Accordingly, any construct in accordance with the invention couldinclude five or six levels, even though those are not explicitlyillustrated herein.

FIGS. 33-39 various views of further exemplary embodiment of a dynamicvertebral column plate system construct 500 in accordance with theinvention, having band-shaped springs 530 and an integral cam element561 adapted and configured to permit a plurality of selectable preloads.The springs 530 can be formed of any suitable material, but inaccordance with one preferred embodiment are a shape memory alloy, suchas Nitinol.

As with the construct 200 illustrated in FIGS. 16-29, a unitary upperplate 510 is provided. Different from that embodiment, however, theupper plate 510 of the construct 500 of FIGS. 33-39 includes a cammingsurface 512 on the underside thereof, as best seen in FIG. 36. When thecams 561 are rotated in line with the central axis of the construct 500,as illustrated in FIGS. 33, 35 and 37, they engage the camming surface512, which then serves to push the outer plate segments 520 a, 520 coutward, away from the intermediate plate 520 b, because the cams 561are rotatably attached to the outer plate segments 520 a, 520 c, and theupper plate 510 is secured to the intermediate plate 520 b. Accordingly,the construct 500 can in implanted with the cams 561 in such anorientation.

Following attachment of the construct 500 to a spinal segment, each ofthe cams 561 can be rotated either clockwise or counter-clockwise. Theshape of the cams 561 is generally oblong, having opposed projections562 extending therefrom, and a socket 569 to engage with a tool foractuating the cams 561. The projections 562 include on their outer ends,detents 564 for catching slideable pins 531 when the cams 561 arerotated clockwise, and inner hooks 566 for catching the slideable pins531 when the cams 561 are rotated counter-clockwise. The two positionsof each cam 561 permit selectable levels of tension of the springs 530,and thus selectable levels of preload applied to a spinal segment. Sucha cam arrangement can be applied to the other embodiments of constructsdescribed herein, including, but not limited to the construct 200described in connection with FIGS. 16-29. As with the construct 200described above, the slideable pins 531 are held in tracks 525, whichare, as embodied, substantially parallel to the inner edges of the endplate segments 520 a, 520 c.

When implanting the construct 500 on a spinal segment, therefore,spacing between adjacent plates is maintained by the cams 561, engagingthe camming surface 512 of the upper plate 510. Following attachment torespective vertebrae, one or more cams 561 can be left in the axialposition, thus essentially providing a static plate at that level. Ifdynamic loading is desired at one or more levels, the respective cam 561is then rotated either clockwise or counter-clockwise, as describedabove, securing the slideable pins 531 in either an intermediateposition or at their most laterally outward extent.

During implantation, a surgeon can apply the smaller of the twoselectable preloads by rotating one or both of the cams 561counter-clockwise, leaving the cam 561 in the position illustrated inFIG. 38. The surgeon can then evaluate whether the preload is sufficientto produce the desired effect, such as in reducing gaps between adjacentvertebrae and fusion materials. If an increased preload is desired, thecam 561 can then be rotated clockwise (by about one-half of a rotation),leaving the cam 561 in the position illustrated in FIG. 39, or viceversa.

It should be noted that in the closed arrangement of the construct 500illustrated in FIGS. 38 and 39, the gaps 591 a and 591 b are fullyclosed because the construct is not connected to a spinal segment. Ifthe construct were connected to a spinal segment, gaps 591 a, 591 bwould remain open indefinitely if the respective cam(s) 561 were left inthe locked position (parallel to the longitudinal axis), and wouldlikely remain open indefinitely to some extent, unless a fusion materialsettled to such an extent after implantation that the inter-vertebralspace contracted by the entire amount of the respective gap 591 a, 591b.

Materials for the components set forth above, including the platesegments 110, 120, can include stainless steels, titanium alloys, memorymetals such as Nitinol, polymeric materials, ceramic materials such assilicon nitride or composite materials, for example.

Devices in accordance with the invention are applicable to any region ofthe vertebral column, such as from the first cervical vertebra (C1) tothe first sacral vertebra (S1). When used in different locations alongthe spinal column, the plate segments 110, 120, engagement members 140,springs 130 and screws 150 are sized according to the size of thevertebral bodies in that region and to the loading conditions that willbe experienced.

Referring now to FIG. 40, there is shown a perspective view of anotherdynamic plate assembly constructed in accordance with a preferredembodiment of the subject invention, and designated generally byreference numeral 600. Plate assembly 600 includes an upper plateportion 610 covering a central plate segment 622, which is bounded byfirst and second outer plate segments 624 and 626. Each of the threeplate segments includes a pair of spaced apart apertures 660. Eachaperture 660 is configured to receive a bone screw 650 for securing theplate assembly 600 to bone structure with a patients body. As describedin more detail below, plate assembly 600 includes structure formechanically retaining the bone screws 650, to prevent them from backingout of the apertures 660 once they have been secured in bone.

Referring to FIG. 41, the structure for retaining the head portion ofthe bone screws 650 associated with the first and second outer platesegments 624, 626 generally U-shaped spring rods 634 and 636. The springrods 634, 636 are independently secured to central plate segment 622 byrespective upstanding yokes 674 and 676. As best seen in FIG. 42, thefree end 634 a of U-shaped spring rod 634 engages an annular groove 652formed in the head portion of screw 650.

Referring back to FIG. 41, the structure for retaining the head portionsof the bone screws 650 associated with the central plate segment 622 isan elongated spring rod 632, which is disposed at an acute anglerelative to a horizontal axis of the central plate segment 622 andsecured to the central plate segment 622 by an upstanding yoke 672. Thefree ends of elongated spring rod 632 may engage an annular grove in thehead of screw 650 as shown in FIG. 42 with respect to the free end 634 aof rod 634, or, in the alternative, as best seen in FIG. 43, the freeends 632 a of elongated spring rod 632 can engage an upper surface ofthe head portion of bone screw 650.

Referring now to FIG. 44, there is shown another embodiment of dynamicplate assembly 600, which includes a shaped central spring rod 722 forretaining the bone screws 650 associated with the central plate segment622. As best seen in FIG. 45, shaped spring rod 722 has an elongatedcentral mounting portion 722 a flanked by oppositely curved screw headretention portions 722 b and 722 c. Central plate segment 622 includesan upstanding yoke 672 for supporting the central mounting portion 722 aof shaped spring rod 722.

The apertures 660 in central plate segment 622 are defined at least inpart by an upstanding peripheral wall 662. A slot 664 is provided in thewall 662 of each aperture 660 in central plate segment 622 toaccommodate the central mounting portion 722 a of the spring rod 722,and a window 666 is formed in the wall 662 of each aperture 660 in platesegment 622 to accommodate passage of the free end of the curvedretention portions of 722 b and 722 c of spring rod 722.

As best seen in FIG. 46, the curved retention portions of 722 b and 722c of spring rod 722 are resilient and deflectable to facilitateengagement with the head portion of a bone crew 650, as shown in FIG.47, wherein, for example, the curved retaining portion 722 b is actuallyengaged within a reception groove 652 formed in the head portion of thebone screw.

Referring now to FIG. 48, there is illustrated a dynamic bone plateassembly 800 that includes at least first and second plate segments 822and 824, which are adapted and configured for movement relative to oneanother from a spaced apart position shown in FIG. 49 to an approximatedposition shown in FIG. 50. A ratcheting pawl member 882 is operativelyassociated with the first plate segment 822 and a rack of ratchet teeth884 are provided on the second plate segment 824 for interacting withthe pawl member 882. This ratchet mechanism allows the first and secondplate segments 822, 824 to move from the spaced apart position of FIG.49 to the approximated position of FIG. 50, while preventing the firstand second plate segments 822, 824 from moving back toward a spacedapart position.

Referring now to FIG. 51, there is illustrated yet another embodiment ofthe dynamic bone plate assembly 600. In this instance, the structure forretaining the head portions of the bone screws 650 associated in each ofthe three plate segments 622, 624, 626 is an elongated spring rod. Moreparticularly, the central plate segments 622 includes a centralelongated spring rod 922 supported on an acute angle within anupstanding yoke 972, the first outer plate segment 624 includes a firsttransverse spring rod 924 supported within an upstanding yoke 974, andthe second outer plate segment 626 includes a second transverse springrod 926 supported within an upstanding yoke 976. In this embodiment ofthe plate assembly 600, the elongate spring rods 922, 924, 926 engagethe upper surfaces of the heads of the bone screws 650 with which theyare associated, as shown for example in FIG. 52 as to spring rod 926.

Referring now to FIG. 53, there is illustrated still another embodimentof the dynamic bone plate assembly 600. In this embodiment, thestructure for retaining the head portions of the bone screws associatedin each of the three plate segments are also elongated spring rods 922,924, 926. However, in this instance, the three elongate spring rods 922,924, 926 extend into or otherwise intersect the screw apertures 660 asshown for example in FIG. 54, and engage retention channels 652 formedin the heads of the bone screws 650 as shown for example in FIG. 55.with which they are associated.

Turning now to FIGS. 56 and 57, there is illustrated a generallyπ-shaped screw retention clip 1010 that is associated with a segment ofa bone plate 1020 for retaining a bone screw 1030 with respect to thebone plate 1020. The retention clip 1010 is adapted and configured tobiasingly or resiliently engage the head 1032 of the bone screw 1030, ora retention channel formed within the head of the bone screw, throughthe side wall 1022 of the plate 1020, to prevent the bone screw 1030from backing out of the aperture 1040 in which it is received. It shouldbe readily appreciated by those skilled in the art that in a plateassembly having multiple plate segments, each having a plurality of bonescrews, there will be provided a respective plurality of retention clips1010, one for each of said bone screws.

Kits in accordance with the invention can be provided, and include arange of plate sizes, springs 130 with varying stiffnesses, engagementmembers with varying stiffnesses and/or shapes, bone screws of varyingsizes, and can include fixed and/or variable angle (polyaxial) screws.Kits can include plates having sizes suitable for cervical and/orthoracic and/or lumbar and/or sacral application.

The devices, systems and methods of the present invention, as describedabove and shown in the appended drawings, provide for vertebral columnplate system constructs and related systems, methods and kits withsuperior properties and versatility, and adaptably enhance fusion of abone graft.

In short, constructs in accordance with the invention can be selectivelydynamic, the dynamism can be passive or active, and if active, a levelof preload can be easily selected. That is, constructs in accordancewith the invention can be used as completely static (being dynamicallyactive at no levels) constructs, can be used as static at one or morelevels and dynamic at the remaining levels, or can be used as dynamic atall levels. Moreover, the selectable dynamism can be active, such as inwhich a preload is applied by the construct, or alternatively passive,in which forces are managed through load sharing between the attachedspinal segment and the construct.

In applications of passive dynamism in accordance with the invention,constructs can be configured to provide a predetermined amount ofresistance to compressive forces in translation and/or bending betweenadjacent plate segments, thereby allowing for a predetermined amount ofload sharing between the construct and the vertebral column segment. Theactive dynamism can include a preload that is selectable, such as byvarying tension in one or more members, such as in one or more springs.Moreover, it should be noted that although the term “spring” is usedherein, it is to be understood that the appearance of such a spring canvary from and is not limited to conventional notions of springs.

It is to be understood that Applicant conceives that features describedherein in connection with one embodiment can advantageously be appliedany other embodiment described herein, even if such feature is notexplicitly described in connection with such embodiment, except wheresuch features are mutually exclusive. That is, it is specificallyconceived that elements of one embodiment are interchangeable with thoseof another embodiment, without limitation, except if such features wouldbe incompatible with other features or necessarily displace anotherfeature, for example.

It will be apparent to those skilled in the art that furthermodifications and variations can be made in the devices, systems andmethods of the present invention without departing from the spirit orscope of the invention. For example, while each of the screw retentionstructures disclosed herein are illustrated as shaped rods that arecircular in cross-section, it is envisioned and well within the scope ofthe subject disclosure that the screw retention rods can havealternative cross-sectional geometries. For example, the rods could havea square cross-section as in the case of a slender bar or staff. Itshould also be understood that these screw retention structures can bemanufactured through a variety of conventional cutting or stampingforming operations that are known in the art.

Furthermore, it should be readily appreciated by those having ordinaryskill in the art that the dynamic plating systems described andillustrated herein are not limited in use or application to spinalstabilization. Rather, it should be appreciated by those skilled in theart that the constructs disclosed herein can be readily modified andused to stabilize other types of bone structure throughout a patient'sbody, including, but not limited to applications involving the dynamicstabilization of bone fractures presented in the limbs of a patient.

What is claimed is:
 1. A vertebral column construct for stabilizing asegment of a vertebral column, comprising: a first plate segment; asecond plate segment connected to the first plate segment; a U-shapedspring connected between the first and second plate segments, whereinthe U-shaped spring has a first end and a second end captured in arecess of the first plate segment and a curved portion extending betweenthe first and second end, the curved portion being captured in a recessof the second plate segment so that the U-shaped spring determines amaximum spacing between the first and second plate segments; a cammounted on the first plate segment to selectively rotate between: alocked position against a cam surface on the second plate segment to seta spacing between the first and second plate segments with a staticload; and an unlocked position so that the U-shaped spring applies adynamic compressive force; and a unitary plate for spanning the firstand second plate segments to enhance stability of the column constructwhile permitting linear translation of the plate segments, wherein theunitary plate forms a male dovetail that couples to the plate segmentsin a female dovetail formed in the plate segments.
 2. The vertebralcolumn construct of claim 1, wherein the U-shaped spring is adapted andconfigured to provide a predetermined preload between the first andsecond plate segments.
 3. An elongated vertebral column construct forstabilizing a segment of a vertebral column, comprising: a first platesegment defining a first groove at a first angle to an axis and a secondgroove at a second angle to the axis; a second plate segment connectedto the first plate segment; a U-shaped spring connected between thefirst and second plate segments, wherein the U-shaped spring has a firstend slideably captured in the first groove and a second end slideablycaptured in the second groove, the U-shaped spring also having a curvedportion extending between the first and second end, the curved portionbeing captured on the second plate segment so that the U-shaped springexerts a net axial compressive force between the first and second platesegments; and a cam mounted on the first plate segment to selectivelyrotate between: a locked position against a cam surface on the secondplate segment to set a spacing between the first and second platesegments with a static load; and an unlocked position so that theU-shaped spring applies a dynamic compressive force.